In many fields of technology, natural science and medicine, analytes in samples must reliably be detected qualitatively and/or quantitatively. This is done in many cases with test elements, which react sensitively to one or more analytes. In particular, it is possible to use test elements which comprise at least one test material that changes at least one measurable property when the analyte is present in the sample, or upon contact with the analyte. These properties may for example, as mentioned in more detail below, be electrical and/or optical properties.
An essential application field of the present invention, albeit one to which the invention is not restricted, is medical diagnosis. For example, the monitoring of blood glucose concentrations is an essential part of daily life for diabetics. In this case the blood glucose concentration must rapidly and simply be determined generally several times per day, so that corresponding medical measures can be implemented if appropriate. In order not to restrict the daily life of a diabetic more than necessary, corresponding mobile instruments are often used which should be simple to transport and handle, so that the blood glucose concentration can be measured rapidly and simply but nevertheless reliably, for example in the workplace or in leisure time. Static instruments may however also be used, for example instruments which are designed for hospitals, medical practices or care institutions.
Various analysis instruments are currently on the market, which sometimes function according to different measurement methods. Various diagnostic methods are employed for this, for example optical or electrochemical measurement methods. The aforementioned test elements, which are usually provided in the form of test strips, are often an essential element of these measurement methods. For example, they may be electrochemical and/or optical test strips. Examples of electrochemical test strips are described, for example, in U.S. Pat. No. 5,286,362. Optical test elements are described, for example in CA 2,050,677. Other types of test elements are also known and may be used in the scope of the present invention, for example implantable test elements (see for example EP 0 678 308 B1). Instead of individual test elements, for example test strips or test tubes, test elements are also known which are held in a magazine or in another type of storage device. For example, a plurality of test elements may be rigidly connected together, for example in the scope of a test disc on which there are a plurality of test fields. Other types of multiple test elements are known, for example in the scope of band cassettes in which a multiplicity of test elements or test fields are arranged on a common band so that they may for example be used in succession. Other embodiments of magazines are drum magazines, in which a plurality of test elements are accommodated in a magazine drum. Other embodiments are also known.
The reliability of the analyte detection plays a crucial role in particular for quantitative detection methods in medical diagnosis. Thus, a range of further decisions generally depend on the result of the detection, for example a decision about insulin medication or a decision about another kind of medical treatment. To this extent efficient quality management is required in the production of the test elements, which reliably prevents defective test elements from being put into circulation or, if they are in circulation, from being used there. This quality management may involve a multiplicity of test methods which can subject the test elements to particular function tests already during the production process, or after production. For example, tests may be carried out which (for example by means of image recognition, electronic measurements, optical measurements or combinations of measurements) check particular functionalities of the test elements and thereby identify defective test elements with a certain probability.
The production of such test elements is generally a mass process, in which a multiplicity of test elements are produced on a large technical scale with a high throughput. When a defective test element is identified, it is therefore generally not possible to reject this test element directly. Methods are therefore known from the prior art in which test elements identified as defective are marked as being defective during or after the production method. Examples of such marking methods are disclosed in US 2004/0048359 A1, where defective regions are marked with a pen or marker. Another method known from the prior art is described in EP 0132790 A2. Here, a multiplicity of test elements are produced on a common band and, after a defect is found, a suitable marking in the form of a color point or a magnetic marking is applied so that the defective test element can subsequently be rejected simply and reliably.
In practice, however, the marking and production methods known from the prior art have numerous disadvantages. For instance, the known marking methods generally employ additional working substances and auxiliary substances, for example inks for the color points, paints, magnetic materials or similar materials. These additional working and auxiliary substances may however interact with the functionality of the test elements, and may for example influence the functionality of a test material (for example a test chemical for the detection of blood glucose or another metabolite). Thus, in general, safety of the working and auxiliary substances used for the marking must extensively be checked and confirmed, for example in order to obtain corresponding statutory approvals.
Another disadvantage of known methods is that many of the known application methods for the working and auxiliary substances, which are used for the marking, are complex and susceptible to error. For example, paints or inks for the marking may be applied by means of a printing method which, however, is per se error-prone in many cases.
Another disadvantage is that in many cases the applied working and auxiliary substances, which are generally used for the marking in the prior art, are applied in liquid form so that a drying time is required after application. In many cases, these drying times of the marking limit the manufacturing speed of the production processes and therefore increase the production costs considerably.